All of the retail brands have listed their deals on a central website, clickmonday.co.nz, which allows shoppers to click through to the retailers' websites to make purchases.

Cate Bryant, an e-commerce consultant who organised Click Monday, said toy retailer Toyco saw a 10-fold increase in its online sales as a result of the event.

"People have voted with their wallets," Bryant said.

She said that by 11pm last night the Click Monday website had had 62,000 visitors and the offers had been viewed 225,000 times.

"The sheer volume of traffic has slowed down quite a few retailer sites, some pretty much to a stop, which will have unfortunately dampened sales," Bryant said.

Toyworld was one of the retailers that struggled with heavy online traffic.

General manager Franco Godinich said the toy retailer's website didn't crash but became very slow after 7pm.

"Click Monday has worked phenomenally [well] for us, but we did have some major pressures on the site," he said. "We're going to continue until midnight tonight with the Click Monday deals just to make sure every customer has a good opportunity to experience our site."

Bryant said she was disappointed that a University of Canterbury marketing expert issued a press release last night criticising the event.

Associate professor Ekant Veer said the Click Monday deals were "not necessarily the cheapest price" and the products available were out of date and end of line.

"As such, Click Monday is more akin to excitement and mob mentality associated with purchasing behaviour, rather than rational savings behaviour or utility maximisation," Veer said.

Bryant said Veer's comments were inaccurate.

While some end of line goods were offered, there were also plenty of new products available, she said.